CN109311472B

CN109311472B - Method for operating a continuously variable transmission in a motor vehicle equipped with a continuously variable transmission

Info

Publication number: CN109311472B
Application number: CN201780037173.2A
Authority: CN
Inventors: A·皮吉尔德; J·洛尔曼; S·施特劳斯; A·A·H·M·范东恩; L·H·J·罗默斯
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2016-06-14
Filing date: 2017-06-14
Publication date: 2022-06-07
Anticipated expiration: 2037-06-14
Also published as: NL1041928B1; WO2018077477A3; JP2019518918A; WO2018077477A2; CN109311472A; JP6945565B2

Abstract

The present disclosure relates to a method for operating a continuously variable transmission (2) for transmitting mechanical energy between an internal combustion engine (1) and drive wheels (3) in a motor vehicle with a continuously variable transmission ratio between a maximum deceleration transmission ratio "LOW" and a maximum acceleration transmission ratio "OD". In one operating mode of the motor vehicle, the engine (1) is shut down by opening the clutch (8) provided between the engine (1) and the drive wheels (3) while the motor vehicle is still moving, and the transmission ratio of the transmission is controlled to a value closer to the maximum acceleration ratio "OD" than to the maximum deceleration ratio "LOW" so that the engine (1) is smoothly restarted by closing the clutch (8) with little notice of the motor vehicle occupants.

Description

Method for operating a continuously variable transmission in a motor vehicle equipped with a continuously variable transmission

Technical Field

The present disclosure relates to a method for operating a continuously variable transmission ("CVT") in a motor vehicle equipped with such a CVT for transmitting mechanical energy between an internal combustion engine ("ICE") and driving wheels of the motor vehicle. CVTs of this kind are well known and provide a transmission ratio between their primary shaft associated with the crankshaft of the ICE and their secondary shaft associated with the axles of the drive wheels, which ratio is continuously varied by the control system of the CVT between a maximum deceleration ratio ("LOW") and a maximum acceleration ratio ("overspeed" or "OD") provided by the respective CVT design. Known CVTs typically include a coupling device, such as a hydraulically actuated wet plate clutch, for correspondingly rotationally coupling or decoupling the ICE with the drive wheels through controlled closing or opening thereof.

Background

One mode of operation of a motor vehicle is known in the art, wherein the ICE is shut down, i.e. stopped, after being disengaged from the rotating drive wheels, while the motor vehicle is still moving. This mode of operation is referred to as idle, freewheeling, cruise, coast and start/stop coasting, the latter terminology will be used subsequently. In this start/stop limp-home mode, not only does the ICE not consume fuel, but the ICE also does not apply a resistive torque to (the movement of) the motor vehicle. The latter feature allows the motor vehicle to travel further and/or longer under its own inertia in the start/stop limp mode, especially compared to the well-known limp mode, i.e. the so-called overrun or limp mode, when the ICE is running. Once operation of the motor vehicle again requires the ICE to apply drive torque for vehicle acceleration, the ICE is (re) started, i.e. (re) started, thereby ending its start/stop coasting operation. The ICE may be restarted by a starter motor of the motor vehicle, or by (re) coupling the ICE to the drive wheels by inertia of the motor vehicle. The latter option is described in german patent application DE102013215101a1, which advantageously reduces the burden on the starter motor of the vehicle. More particularly, in this latter option, the coupling device is initially controlled to transfer (only) the ICE restart torque, i.e. by sliding engagement of portions thereof, to gradually accelerate the crankshaft of the ICE until the ICE can be started by igniting the air/fuel mixture provided to it, i.e. until it is self-running. Thereafter, rotation of the ICE crankshaft is synchronized with rotation of the drive wheels, the clutch is fully engaged, and forward drive operation of the drive train is resumed.

Disclosure of Invention

The present disclosure also relates to the latter option of re-starting the ICE by re-coupling the ICE to the drive wheels. According to the present disclosure and prior to such re-coupling, the CVT is controlled to provide a transmission ratio closer to the OD ratio than the LOW ratio. Thus, this CVT ratio at ICE restart is selected independently of the CVT ratio at the start of the start/stop coasting operation of the motor vehicle.

According to the present disclosure, the particular method of operation of the motor vehicle and its CVT has, among other things, the following advantages: the torque required for ICE restart, i.e., ICE restart drag torque, is reduced on the CVT to a lower drag torque level at the drive wheels. Therefore, the deceleration of the motor vehicle due to the ICE restart, i.e., due to such a drag torque, is advantageously made smaller. Thus, not only is the comfort of the motor vehicle occupants improved, but also the dynamic performance of the motor vehicle is improved. After all, an ICE restart is performed to (subsequently) accelerate the motor vehicle, so that it is preferred to minimize a (previous) deceleration of the motor vehicle during the ICE restart.

In practice, the range of transmission ratios provided by a CVT is more or less symmetrically distributed around a1 to 1 ratio ("mid" or "MED"), which is generally the case in the well-known belt-pulley type CVTs. Thus, according to the present disclosure, the CVT is controlled to a transmission ratio between 1 and the OD ratio. Alternatively, the variator ratio range of the CVT may be measured linearly between 0% and 100%, with the LOW ratio corresponding to a value of 0% of the range, the MED ratio corresponding to a value of 50% of the range, and the OD ratio corresponding to a value of 100% of the range. In the latter definition, the CVT is controlled to linearly measure the gear ratio within a sub-range from 50% to 100% of the gear ratio range according to the present disclosure.

In a more detailed embodiment of the above-described CVT operating method according to the present disclosure, the CVT is controlled to a variator ratio value of greater than 60%, preferably greater than 75%, over the linearly measured variator ratio range.

After the above-described re-coupling of the ICE to the drive wheels for re-starting the ICE, the ICE may again be decoupled from the drive wheels to allow the ICE, in particular its crankshaft, to accelerate and stabilize quickly and independently before it is finally and fully coupled to the drive wheels by closing the coupling device. According to the present disclosure, and during such independent acceleration of the ICE, the transmission ratio of the CVT is controlled from the CVT transmission ratio selected at ICE restart towards the LOW ratio, in particular controlled to provide a transmission ratio closer to the LOW ratio than to the OD ratio. This latter method of operation of the motor vehicle and of its CVT has, according to the present disclosure, among other things the following advantages: after the ICE is ultimately coupled to the drive wheels, the torque generated by the ICE is increased over the CVT to a higher drive torque level at the drive wheels to improve the acceleration performance of the motor vehicle.

In a more detailed embodiment of the above-described CVT operating method according to the present disclosure, the CVT is controlled to a variator ratio value of less than 90%, preferably less than 85%, of the linearly measured variator ratio range. This latter detailed embodiment is for this reason: as the drag torque at the drive wheel becomes smaller by applying a gear ratio closer to the OD ratio, its effect on improvement of the comfort of the vehicle occupant is reduced. In this latter aspect, below a certain level of drag torque at the drive wheels, further reduction thereof will generally not be noticeable. At the same time, the closer the CVT transmission ratio is to the OD ratio, the less torque is available at the drive wheels for desired acceleration of the motor vehicle after the ICE restart. Furthermore, the ICE is restarted not only in response to an acceleration request, such as the driver of the vehicle engaging an accelerator pedal, but also in response to a deceleration request, such as the driver of the vehicle engaging a brake pedal. In the latter case, an additional engine braking effect may be required during and after (re) engagement of the clutch. However, the closer the CVT speed ratio is to the OD ratio, the less effective this engine braking effect.

Based on these latter technical considerations, the CVT speed change ratio at the ICE restart preferably satisfies the above-described upper limit as an optimum value between minimizing the drag torque before the vehicle accelerates and maximizing the subsequent acceleration performance or engine braking effect. More particularly, in the latter aspect, the actual applicable subrange of the CVT ratio at ICE restart is between 66% and 83% of the linearly measured ratio range, where values of 80% represent widely applicable optimal values. Still, such an optimum value of CVT transmission ratio at ICE restart may vary depending on vehicle/driveline characteristics and/or driver type/behavior, and may therefore be obtained during initial vehicle calibration activities and/or adjusted during vehicle operation.

In another more detailed embodiment of the above CVT operating method according to the present disclosure, the gear ratio achieved by controlling the CVT during the start/stop coasting is related to the instantaneous vehicle speed. For example, at least at relatively low vehicle speeds, in particular below 30km/h, the CVT speed ratio at ICE restart may be selected between 80% and 100% of the linearly measured speed ratio range, whereas at high vehicle speeds, in particular above 70km/h, the CVT speed ratio at ICE restart may be selected between 50% and 80% of the linearly measured speed ratio range. This particular embodiment is due to this consideration: ICE restart is more pronounced at lower vehicle speeds, and therefore gear ratios increasingly closer to the OD ratio are required to ensure passenger comfort. Thus, according to the present disclosure, the CVT transmission ratio at ICE restart is preferably directly, but inversely, related to the vehicle speed during start/stop coasting.

Drawings

The method for operating a continuously variable transmission according to the present disclosure will now be further elucidated by way of example with reference to the following drawings, in which:

fig. 1 shows in a highly schematic manner a known continuously variable transmission which is applied in and as part of a drive train of a motor vehicle;

FIG. 2 graphically illustrates a range of transmission ratios of a known continuously variable transmission;

FIG. 3 graphically illustrates one embodiment of a method for operating a continuously variable transmission in accordance with the present disclosure in connection with transitioning between two operating modes of a known motor vehicle drive train; and

FIG. 4 graphically illustrates one embodiment of a method for operating a continuously variable transmission in accordance with the present disclosure with respect to such a transition between the two operating modes.

Detailed Description

Fig. 1 shows an example of a known drive train of a motor vehicle, with an internal combustion engine ("ICE") 1, a continuously variable transmission ("CVT") 2 and drive wheels 3, which are usually formed by two or four drive wheels 3 of the vehicle. A coupling device, such as a wet plate clutch 8, is included in the drive train to rotationally couple or decouple the ICE 1 to or from the drive wheels 3, respectively, by controlled closing, opening thereof. Typically, a gear train (not shown) comprising a differential gearing is included between the secondary shaft 6 and the wheel axle 7. Typically, the CVT 2, the clutch 8 and the gear train share a single housing (not shown).

In the drive train, the crankshaft 4 of the ICE 1 is rotationally coupled to the primary shaft 5 of the CVT 2, and the secondary shaft 6 of the CVT 2 is rotationally coupled to the axle 7 of the drive wheel 3. The CVT 2 provides a continuously variable transmission ratio between its primary shaft 5 and its secondary shaft 6, i.e. between the ICE crankshaft 4 and the driven axle 7, within the range of possible transmission ratios between the maximum decelerated transmission ratio ("LOW ratio") and the maximum accelerated transmission ratio ("overspeed" or "OD ratio") of the CVT 2.

In the example shown, the CVT 2 is provided with a drive belt 11 which is wound around an adjustable primary pulley 12 on the CVT primary shaft 5 and an adjustable secondary pulley 13 on the CVT secondary shaft 6. The

pulleys

12, 13 define the primary running radius and the secondary running radius of the drive belt 11, respectively, under the influence of the respective hydraulic pressure exerted in their respective pressure chambers 14, 15. In fig. 1, the CVT 2 is shown in a state where the rotation speed of the drive wheels 3 is decelerated with respect to the rotation speed of the ICE 1.

In the example shown, the clutch 8 is included between the ICE crankshaft 4 and the CVT primary shaft 5, but it may also be provided on the secondary shaft 6 side of the CVT 2. Furthermore, in the example shown, the clutch 8 comprises two friction plates 9, which friction plates 9 can be pressed together under the effect of a hydraulic engagement pressure applied in a clutch pressure chamber 10 of the clutch 8 to gradually and controllably synchronize the rotation of the ICE crankshaft 4 with the rotation of the CVT main shaft 5.

The known drive train is provided with a control system 16 for controlling its functions, such as the pressure levels in the clutch pressure chamber 10 and the CVT pressure chambers 14, 15, respectively, which latter two pressure levels determine not only the torque that can be transmitted through the CVT 2, but also its transmission ratio. In addition, the control system 16 utilizes a plurality of input signals S1-3, such as actual hydraulic pressure, actual rotational speed, ICE torque level, and the like.

Fig. 2 shows a range of transmission ratios provided by the CVT 2 in a graph, in which the rotational speed RSP of the CVT primary shaft 5 is plotted on the horizontal axis and the rotational speed RSS of the CVT secondary shaft 6 is plotted on the vertical axis. In this graph, the lower solid line LOW represents the maximum deceleration speed ratio of the CVT 2, and the upper solid line OD represents the maximum acceleration speed ratio of the CVT 2. The transmission ratio of the CVT 2 may take any value between these two extreme values LOW and OD. For example, the broken line MED represents a middle speed ratio of the CVT 2, more specifically, a speed ratio at which the main shaft rotation speed RSP is equal to the secondary shaft rotation speed RSS. In the context of the present disclosure, the range of the speed ratio of CVT 2 is linearly measured, where speed ratio LOW is defined as a value corresponding to 0%, speed ratio MED has a value of 50%, and speed ratio OD has a value of 100%.

With respect to known motor vehicles, it has been suggested in the art to improve the operating efficiency of the ICE 1 by disengaging and shutting down it when engine torque is not required (i.e. neither positive torque, i.e. driving torque, nor negative torque, i.e. drag torque, is required), but also when the motor vehicle itself is still moving. The latter operating mode is hereinafter indicated as start/stop coasting and may for example be engaged when the motor vehicle is driving downhill, in particular on a gentle slope where engine braking is not required. In a vehicle, a condition where ICE torque is not required may be associated with the vehicle driver having released the accelerator pedal without engaging the brake pedal or the clutch pedal such that the driving torque demand is zero.

The start/stop coasting operating mode is ended by the motor vehicle being completely stopped or by ending the torque demand of the idling phase of the motor vehicle, i.e. by the demand of the resistance torque or the demand of the driving torque required to provide the engine braking effect. At least in the case of such a drive torque demand, the ICE 1 is (re-) started by (re-) coupling the crankshaft 4 of the ICE 1 via the CVT 2 to the rotating drive wheels 3 by closing the clutch 8. In particular, this decoupling is often carried out in three phases, namely:

a first phase I, in which the clutch 8 is only partially engaged, i.e. controlled to be able to slip and to (only) deliver the (resistive) torque required to restart the ICE 1, in particular for rotating the ICE crankshaft 4, while fuel and air are supplied into the ICE 1 and ignited within the ICE 1;

a second phase II, in which the clutch 8 is again at least partially open, in which the rotational speed of the ICE crankshaft 4 is increased by the ICE 1 itself, in particular until such crankshaft speed CRS corresponds to the speed PRS of the CVT primary shaft 5; and

a third phase III, in which the clutch 8 is fully engaged, i.e. controlled to establish a slip-free drive between the ICE crankshaft 4 and the CVT main shaft 5.

The above-described processes of disengaging and shutting down and starting and recoupling of the ICE 1 are schematically illustrated in fig. 3 by time curves of the rotational speed RSC of the ICE crankshaft 4, the rotational speed RSP of the CVT primary shaft 5, the rotational speed RSS of the CVT secondary shaft 6 and the engagement pressure EPC of the clutch 8 (i.e. the pressure exerted in the clutch pressure chamber 10 of the clutch 8 which can vary between zero (i.e. the clutch is not engaged; no torque is transferable) and a maximum level (i.e. the clutch provides its maximum torque transfer capacity)).

In FIG. 3, at a certain point in time t₀By opening the clutch 8 (in which the clutch engagement pressure EPC is reduced to zero) and by shutting down the ICE 1 (in which the crankshaft speed RSC is from before the start/stop coasting operation, i.e. at the time point t₀Previously corresponding to a reduction of CVT spindle speed RSP to zero) initiates the start/stop limp-home mode of operation of the motor vehicle.

Assuming that the motor vehicle is running on a flat road, the vehicle speed, the rotation speed of the drive wheels 3, and the rotation speed of the CVT secondary shaft 6 (i.e., RSS) are gradually reduced during the start/stop coasting. Further, during the start/stop coasting, according to the present disclosure, the speed ratio of the CVT 2 is controlled to a specific predetermined value closer to the OD ratio rather than closer to the LOW ratio. In the specific example of fig. 3, the CVT speed ratio is before coasting from start/stop, i.e., time t₀The previous value of 40% of the linearly measured ratio range of the CVT 2 is increased to a value of 76% of the range, whereby the CVT spindle speedRSP decreases relative to CVT secondary shaft speed RSS.

At a later point in time t₁The drive torque demand is again generated in the drive train, and in response the start/stop limp-home mode of operation is ended by restarting the ICE 1 by reconnecting the ICE crankshaft 4 to the CVT main shaft 5 by means of (re-) engagement of the clutch 8. According to the present disclosure, because the variator ratio of the CVT 2 is between MED and OD, the torque required for the ICE 1 to restart is advantageously reduced on the CVT to a lower torque level at the drive wheels 3. Thus, the deceleration of the motor vehicle due to ICE restart, i.e. due to such drag torque, is advantageously reduced, thereby enhancing the comfort of the motor vehicle occupants.

After ICE 1 restart, at time t in FIG. 3₂Alternatively, the clutch 8 can be opened again by reducing the clutch engagement pressure EPC again to zero and the ICE crankshaft 4 is accelerated rapidly by the ICE 1 itself, i.e. advantageously without applying a drag torque on the drive wheels 3. More specifically, the ICE crankshaft 4 is accelerated such that it is at time t in FIG. 3₃Its rotational speed RSC is at least close to the CVT spindle rotational speed RSP. Thereafter, by applying the maximum clutch engagement pressure EPC, the clutch 8 can be closed quickly and smoothly. When the clutch 8 is at time t₂And time t₃According to the present disclosure, the transmission ratio of the CVT 2 is preferably adjusted between LOW and MED, as shown in fig. 3. Thus, after the clutch 8 is finally closed, i.e. at time t₃The ICE 1 drive torque is then advantageously amplified on the CVT to a higher torque level at the drive wheels 3. Therefore, the acceleration performance of the motor vehicle after the start/stop coasting operation mode ends becomes advantageously high.

An example of the above-described process of disengaging and shutting down and starting and re-coupling the ICE 1 according to the present disclosure is also schematically illustrated in the graph of fig. 4. In fig. 4, the rotational speed RSS of secondary CVT shaft 6 is plotted on the vertical axis against the rotational speed RSP of primary CVT shaft 5 on the horizontal axis. In the start/stop coasting mode of operation, the transmission ratio of the CVT 2 is controlled by any ratio value SR0 applicable at the start of the start/stop coasting mode of operation to the predetermined value SR1 of 76% of the linearly measured CVT transmission ratio range. Therefore, the actual operating point of the CVT 2 is changed from SR0 'to SR1', as indicated by arrow a in fig. 4.

During the start/stop coasting operation mode, the rotation speed RSS of the CVT secondary shaft 6 coupled to the drive wheels 3 is gradually reduced in accordance with the reduction in the vehicle speed, so that the instantaneous operation point SR1 ″ of the CVT 2 moves downward along the broken line corresponding to the selected shift ratio value SR1, as indicated by the arrow B in fig. 4. In this latter aspect, according to a more detailed embodiment of the present disclosure, the value of the speed change ratio selected during the start/stop coasting may be selected to be increased relative to such a reduced rotation speed RSS of the CVT secondary shaft 6, as indicated by arrow C in fig. 4.

It should be noted that the minimum rotation speed RSP of the CVT primary shaft 5 is preferably applied, i.e. the CVT speed ratio selected during start/stop coasting is limited with respect to the rotation speed RSS of the CVT secondary shaft 6, as shown in fig. 4 with arrow E, for example at a main shaft rotation speed RSP of 800 rpm. After all, when the clutch 8 is at time t₁When engaged to (re) start the ICE 1, a sufficient rotational speed RSC of the crankshaft 4 must be achieved. More particularly, in the latter respect, a practically applicable subrange of said minimum rotation speed RSP of the CVT main shaft 5 is between 700 and 1000 rpm.

Further in accordance with the present disclosure, after the ICE 1 has been (re) started, the speed ratio of CVT 2 is preferably controlled from the CVT speed ratio SR1 selected at ICE restart toward another speed ratio SR2 that is closer to the LOW ratio than to the OD ratio, as indicated by arrow D in fig. 4. This has the advantage that: the torque generated at the ICE 1 is increased at the CVT 2 to a higher driving torque level at the driving wheels 3 to improve the acceleration performance of the motor vehicle. However, considering that the further speed change ratio SR2 is controlled closer to the LOW ratio, the higher the rotation speed RSP of the CVT main shaft 5 and the longer it takes to synchronize the rotation speed RSC of the ICE crankshaft 4 with this rotation speed RSP. Thus, although the subsequent acceleration performance of the vehicle can be increased by selecting the other speed change ratio SR2 closer to LOW, the actual acceleration of the vehicle is thereby increasingly delayed. Therefore, it may be necessary to limit such downshifting of the CVT 2 from the transmission ratio SR1 to the other transmission ratio SR2 to provide the best possible practical acceleration of the vehicle. More specifically, in the latter aspect, a practically applicable sub-range for the downshift is between 30% and 60% of the total speed ratio range of the CVT 2 between LOW and OD.

Referring back to fig. 1, noting the arrangement of the clutch 8 between the ICE crankshaft 4 and the CVT main shaft 5, when the clutch 8 is open and the ICE 1 is stopped in the start/stop coasting mode of operation, the

pulleys

12, 13 and the belt 11 of the CVT 2 continue to rotate with the drive wheels 3. The advantage of this drive train arrangement is that the transmission ratio of the (rotating) CVT 2 can also be freely and reliably controlled, i.e. adjusted, during the start/stop coasting. However, if the clutch 8 is alternatively arranged between the secondary shaft 6 and the axle 7 of the CVT 2, the CVT 2 is in a parked state together with the ICE 1 during start/stop coasting. When the CVT 2 is standing still, the static friction between the belt 11 and the

pulleys

12, 13 is significantly higher than the dynamic friction therebetween in the rotating CVT 2, and the gear ratio control is seriously hindered or completely impossible.

Especially in the latter drive train arrangement, it is preferred according to the present disclosure that at the start of the start/stop coasting operation mode of the motor vehicle, the ICE 1 is not stopped simultaneously with the opening of the clutch 8, but first the transmission ratio of the CVT 2 is controlled to the value between MED and OD, and only thereafter the ICE 1 is completely stopped. Of course, the shutdown of the ICE 1 requires some time, for example, to run down its crankshaft 4 to a complete stop, during which the gear ratio control of the CVT 2 is still possible. However, in general, in order to complete the transmission ratio control, it is necessary to extend this turn-down time, albeit only for a limited time and only in a limited amount, by continuing to supply fuel to the ICE 1 after the clutch 8 is opened.

It is further noted that the drive train, in particular the control system 16 thereof, is typically provided with at least one pump for generating a flow of pressurized hydraulic medium, in particular for achieving said pressure levels in the clutch and CVT pressure chambers 10, 14, 15. In the sense of start/stop coasting operation of the drive train, such a pump must (also) be operable when the ICE 1 is stopped, in order to be able to pressurize the CVT pressure chambers 14, 15 and to pressurize the clutch pressure chamber 10, thus being able to close the clutch 8 at the end of the start/stop coasting operation to (re) start the ICE 1. Thus, the at least one pump of the known control system 16 may be driven by an electric motor, i.e. electrically. The size of the at least one pump of the known control system 16 is relatively large and the electrical power required to operate it is relatively high, making the known control system 16e relatively expensive to manufacture and/or operate. These requirements are exacerbated in the sense of the present disclosure, since not only the clutch 8 is closed but also the transmission ratio of the CVT 2 is controlled when the ICE 1 is stopped.

According to the present disclosure, the control system 16 is preferably provided with a hydraulic accumulator which is filled with a hydraulic medium and which is pressurized by the at least one pump during start/stop coasting operation of the drive train. The hydraulic accumulator is then used to supply this flow of pressurized hydraulic medium at least at the end of the start/stop limp-home mode of operation to support the electric pump in restarting the ICE 1 and pressurizing the CVT pressure chambers 14, 15 by closing the clutch 8 through pressurizing the clutch pressure chamber 10.

In addition to all of the details of the foregoing description and accompanying drawings, the present disclosure also relates to and includes all of the features of the appended claims. Reference signs in the claims do not limit their scope, but are provided merely as a non-limiting example of corresponding features. The claimed features may be applied individually, as appropriate, in a given product or in a given process, but any combination of two or more such features may also be applied therein.

The invention represented by this disclosure is not limited to the embodiments and/or examples explicitly mentioned herein, but also includes modifications, improvements and practical applications thereof, especially those modifications, improvements and practical applications that would occur to one skilled in the art.

Claims

1. A method for operating a continuously variable transmission (2) in a drive train of a motor vehicle having an internal combustion engine (1), a coupling device (8) for rotationally coupling or uncoupling the internal combustion engine and the drive wheels, respectively, by controlled closing or opening thereof, a drive wheel (3) and a transmission (2), the continuously variable transmission (2) being used for rotationally coupling a primary shaft (5) of the transmission (2), which is coupled to a crankshaft (4) of the engine (1), with a secondary shaft (6) of the transmission (2), which is coupled to an axle (7) of the drive wheel (3), at a variable transmission ratio between a maximum reduction transmission ratio (LOW) and a maximum acceleration transmission ratio (OD), the drive train being provided as part of its operation: -it is possible to open the coupling device (8) and, with the opening of the coupling device (8), subsequently simultaneously shut down, i.e. stop, the engine (1) and, at a later moment, open, i.e. restart, the engine (1) by closing the coupling device (8), in which method, before closing the coupling device (8), the transmission ratio of the transmission (2) is controlled to be closer to said maximum acceleration transmission ratio (OD) than to said value of the maximum deceleration transmission ratio (LOW) (SR1), and in which method, after opening the engine (1) by partially closing the coupling device (8), the coupling device (8) is subsequently opened again temporarily, to allow the engine to accelerate and then only finally be fully coupled to the drive wheels by fully closing the coupling device, characterized in that, when the coupling device (8) is temporarily opened again before being fully closed, -adjusting the transmission ratio of the transmission (2) from a controlled value (SR1) controlled during partial closure of the coupling device (8) in the direction of said maximum deceleration transmission ratio (LOW).

2. Method for operating a continuously variable transmission (2) according to claim 1, wherein the transmission ratio of the transmission (2) is adjusted from a controlled value (SR1) controlled during partial closure of the coupling device (8) in the direction of said maximum deceleration transmission ratio (LOW) to a value between 30% and 60% of the total range of transmission ratios of the transmission (2).

3. Method for operating a continuously variable transmission (2) according to claim 1 or 2, wherein said controlled value (SR1) of the transmission ratio of the transmission (2) is increased with respect to the speed of deceleration of the motor vehicle at least when the vehicle speed falls below a minimum threshold speed, before the coupling device (8) is partially closed to switch on the engine (1).

4. Method for operating a continuously variable transmission (2) according to claim 1, wherein said controlled value (SR1) of the transmission ratio of the transmission (2) lies between a value of 66% and a value of 85% of the transmission ratio spread of the transmission (2) from said maximum deceleration ratio (LOW), representing a value of 0% of the transmission ratio spread, to said maximum acceleration ratio (OD), representing a value of 100%.

5. Method for operating a continuously variable transmission (2) according to claim 1, wherein said controlled value (SR1) of the transmission ratio of the transmission (2) substantially corresponds to a value of the transmission ratio spread of the transmission (2) from said maximum deceleration transmission ratio (LOW) representing a value of 0% of the transmission ratio spread to 80% of said maximum acceleration transmission ratio (OD) representing a value of 100%.

6. Method for operating a continuously variable transmission (2) according to claim 1, 4 or 5, wherein after starting the engine (1) by closing the coupling (8) and subsequently temporarily opening the coupling (8) again, the transmission ratio of the transmission (2) is adjusted to a value (SR2) closer to the maximum deceleration transmission ratio (LOW) than to the maximum acceleration transmission ratio (OD).

7. Method for operating a continuously variable transmission (2) according to claim 1, 4 or 5, wherein in the drive train with the coupling device (8) positioned between the secondary shaft (6) of the transmission (2) and the wheel axle (7) of the drive wheel (3), the gear ratio of the transmission (2) is first controlled to said controlled value (SR1) at the same time and/or after the coupling device (8) is opened, before the engine (1) is stopped.

8. Method for operating a continuously variable transmission (2) according to claim 1, 4 or 5, wherein the drive train is further provided with: an electric pump for supplying a hydraulic medium for closing the coupling device (8) and for controlling the transmission ratio of the transmission (2); and a hydraulic accumulator for storing and supplying a hydraulic medium, wherein at least a part of the hydraulic medium supplied by the electric pump is stored in the hydraulic accumulator when the engine (1) is shut down before the coupling device (8) is closed, wherein the coupling device (8) is subsequently closed by means of the hydraulic medium supplied by the hydraulic accumulator.